The contribution of mononuclear phagocytes in host response to cancer is determined in large part through the pattern of gene expression induced in response to stimuli encountered in the tumor microenvironment. Control of macrophage gene expression in response to prototypic pro-inflammatory (IFNgamma and LPS) or anti-inflammatory agents (IL-10 and TGFbeta) results from the integration of multiple intracellular signals that operate at both transcriptional and post-transcriptional levels. Current knowledge of post-transcriptional regulation of specific mRNA stability is limited. AU rich sequence elements (AREs) in the 3' untranslated regions (UTRs) of many cytokine and chemokine mRNAs in concert with ARE-specific RNA binding proteins lead to rapid mRNA decay. We and others have shown that pro-inflammatory or anti-inflammatory stimuli can stabilize or destabilize, respectively, selected chemokine mRNAs particularly KC (mouse CXCL1). These findings lead to the general hypothesis that post-transcriptional control of transiently expressed inflammatory genes involves the induced stabilization of unstable mRNAs through a process that operates in sequence specific fashion. Anti-inflammatory agents act by antagonizing this response. At present multiple features of this model remain undefined. These include (a) the sequence determinants for stimulus-dependent response, (b) how signaling pathways initiated by stabilizing and/or destabilizing agents are integrated and coupled with control of mRNA stability, (c) which steps in mRNA decay are altered by stabilizing or destabilizing stimuli and (d) how ARE-binding proteins couple signaling events to effector mechanisms responsible for the changes in mRNA decay. We now propose to address these issues as a further test of the hypothesis by performance of the following specific experimental aims. 1. Evaluate the sequence basis for ARE-dependent, stimulus-mediated control of mRNA stability. 2. Evaluate signaling pathways involved in the control of mRNA stability by LPS, IL-10 and TGFbeta. 3. Identify the mRNA decay mechanisms that are subject to stimulus-dependent modulation. 4. Determine the role of known ARE/RNA binding proteins in LPS-induced stabilization and IL-10 or TGFbeta-mediated destabilization